Can't Get My son's Computer to Connect

Hello, I got my son a Desktop and can't get it connect to Internet or to my router. I have it hook up wired it keeps giving me a error message. I checked the cable it works . I have tried uninstalling & reinstalling the Router program on my computer no affect. Both computers have Window 7 . Is there something I can download on my computer and transfer on disc or is this a hardware problem? Any Ideas what I can do would be appreciated . Thank You